The present invention relates to an optical transmission equipment and an optical network therefor, and more particularly to an optical transmission equipment using a wavelength selective switch and an optical network therefor.
In switching for each of wavelengths at a transmission equipment node in a wavelength division multiplexing (WDM) optical network in which optical signals of plural wavelengths are multiplexed within one optical fiber, an optical add/drop multiplexer (OADM) that demultiplexes and receives a part of wavelength within the plural wavelengths, and adds and transmits a part of wavelength within the plural wavelengths is commercially introduced, and is mainly being used in the optical network. In the future, development is expected of a wavelength cross-connect (WXC) equipment using a wavelength selective switch that not only demultiplexes and receives a part of wavelength, but also distributes and transmits an arbitrary wavelength to plural routes, and adds a part of wavelength, and distributes and transmits the added wavelength to an arbitrary route, with the prospect of the wavelength cross-connect equipment to be diversified into the optical network.
Referring to FIGS. 1A to 1D, the topology of a wavelength control optical network using the OADM and the WXC will be described. FIGS. 1A to 1D are block diagrams showing the optical network. For simplification of drawing, transmission/reception in one direction is shown in FIGS. 1A to 1D. Also, FIGS. 1A and 1B show only one node. Add and drop are represented by typical nodes. In FIGS. 1A to 1D and subsequent figures, bold solid lines represent an optical signal that is equal to larger than 1 in the number of wavelengths, and thin solid lines represent an optical signal that is 1 in the number of wavelength.
The OADM optical network is formed of a linear or ring network as shown in FIGS. 1A and 1C. The WDM signal into which plural wavelengths are multiplexed conducts the operation of drop, add, and through in each of the wavelengths by an OADM equipment 100, and transmits or receives the optical signal between the respective nodes.
The WXC node of the WXC optical network is applied to a node of a mesh network or a node of connection between the rings as shown in FIGS. 1B and 1D. A WXC equipment 20 conducts the operation of drop, add, and through in each of the wavelengths of the WDM signals that come from plural routes, distributes the WDM signals in the plural routes, and transmits or receives the optical signal between the respective nodes.
Referring to FIG. 1D, nodes other than between-ring connection nodes are formed of the OADM equipments 100, but may be formed of the WXC equipment 200. Referring to FIGS. 1A to 1D, a drop optical signal is output to a first optical transponder not shown. On the other hand, an add optical signal is an output signal of a second optical transponder (not shown) having a predetermined wavelength.
Referring to FIG. 2, the configuration of the OADM equipment will be described. FIG. 2 is a block diagram of the OADM equipment. Referring to FIG. 2, the WDM signal that is a wavelength multiplexed signal is demultiplexed, dropped or goes through in each of the wavelengths by a demultiplexer (DMUX) 11. Also, the added wavelengths are multiplexed with the through signals by a multiplexer (MUX) 12, and then transmitted. The OADM equipment 100 has a configuration of two routes/directions of a route a and a route b. In this example, the through signal is demultiplexed in each of the wavelengths, one by one. For that reason, when the transmitted optical signal is deteriorated by the low OSNR (optical signal to noise ratio), photoelectric conversion and electro-optical conversion are conducted by a regenerator (RGN) 3 to newly transmit an optical signal.
However, in the WXC equipment using the wavelength selective switch, because there exists no port where the through signal is demultiplexed wavelength by wavelength, no regenerator cannot be inserted, as disclosed in JP 2003-125430A.